KERS is pretty relevant to road technology, yes.
Which is why the Prius has had "KERS" for over a decade, now.
But there are some teams, like Williams, who are looking to commercialize what they've learned with KERS, so it's not completely greenwashing.
As for rules change, the engine rule change may cost something now, but it is pretty important for F1 to attract more manufacturers and engine suppliers. When we all thought that the new engines would be I4s, mass manufacturers started expressing interest in returning. Big, powerful V8s are hardly road relevant nowadays, but smaller turbocharged engines are.
To minimize costs, they've started stabilizing the aero rules. Very minimal changes between seasons this year, mostly clarifications on what is legal and what is not.